Two quality second-half finishes from Yakubu secured Middlesbrough's place in the FA Cup quarter-finals despite a poor performance against Championship Preston.

North End, whose 25-match unbeaten record was brought to an end, had the better of the game but could not convert their dominance into clear chances.

And Yakubu made them pay with a half-volley following a flick-on from Jimmy-Floyd Hasselbaink just after the break and then a low header as he arrived unmarked to meet Stewart Downing's free-kick at the far post.

Preston, 10 league places below their visitors, were keen to show they were not intimidated at facing Premiership opposition and showed plenty of early attacking intent.

David Nugent's first real touch saw him get around youngster Tony McMahon and cross to the near post where Chris Sedgwick flicked straight at Mark Schwarzer.

With Boro employing five in midfield, Preston boss Billy Davies started with a narrow three-man unit of Paul McKenna, Brian O'Neil and Callum Davidson and ensured the visitors never had time to settle and lone striker Yakubu was starved of possession.

Playing on the left of a three-pronged attack, Nugent was a constant menace and, breaking from deep, had a shot deflected narrowly wide of Schwarzer's goal in the 12th minute.

After full-back Matt Hill won a challenge with George Boateng, who had overcome an ankle problem to feature, Nugent again forced a save from Schwarzer with an effort from 25 yards.

Boro forays into North End territory were rare and although his side were well on top, Davies was given a stern warning by referee Phil Dowd after his angry reaction to a challenge by Yakubu on the impressive Youl Mawene.

Steve McClaren's side finally made work for their former goalkeeper Carlo Nash in the 31st minute but he had no trouble at all dealing with a crossed free-kick from Downing following a high challenge from McKenna on Boateng.

As Davis won another tussle with Yakubu, Preston striker Patrick Agyemang beat McMahon with ease and his run on goal was only halted by a timely tackle by Chris Riggott.

There was even more concern for McClaren as midfielder Fabio Rochemback was carried off in added time at the end of the first half following a tackle from Davidson.

The subsequent free-kick saw Emanuel Pogatetz head straight at Nash from Downing's cross.

McClaren had clearly not seen enough he liked and Hasselbaink came on for McMahon at the break to partner Yakubu in attack, with Stuart Parnaby dropping back to right-back.

And six minutes after the break, Yakubu punished the North End defence with his side's first shot on target.

A long throw from Franck Quedrue was flicked on by Hasselbaink and Yakubu blasted a half-volley past Nash from the edge of the area.

Boro immediately began playing with a lot more confidence and were passing the ball much more comfortably, although Agyemang caused them a couple of moments of worry with two long-range shots; one that flew wide and another that was saved low by Schwarzer.

Preston refused to be rattled and as they pressed for an equaliser, Nugent also rifled an effort narrowly off target.

In the 65th minute, Schwarzer was at full stretch to keep out a Mawene header from McKenna's crossed free-kick, given for a foul by Yakubu on Sedgwick.

Boro were furious when Hasselbaink tangled with Hill and failed to run onto a fine throughball from Mendieta but that was only a short break from their defending.

With 15 minutes remaining, Schwarzer palmed away McKenna's corner only for Boateng to be robbed by Davidson, whose cross picked out Nugent, only for the striker to fail to make a proper connection on his header.

But with 13 minutes remaining, Yakubu doubled the lead to all but seal his side's place in the last eight.

Following Davidson's foul on Quedrue, Downing's lofted free-kick picked the Nigerian out at the far post and his stooping header had too much on it for Nash to keep out.

While North End had refused to be put off by the opening goal, they never looked like making a dent on Boro's two-goal advantage and, shored up by substitute Gareth Southgate at the back, the visitors ruthlessly closed the game out with a minimum of fuss.

Teams:

Preston Nash, Mears, Mawene, Davis, Hill,Sedgwick (Lewis Neal 67), McKenna, O'Neil (Dichio 68),Davidson, Agyemang (Lucketti 82), Nugent.

Subs Not Used: Hibbert, Ward.

Booked: Mawene, Davidson.

Middlesbrough Schwarzer, McMahon (Hasselbaink 45), Riggott,Pogatetz, Queudrue, Parnaby, Mendieta, Boateng,Rochemback (Cattermole 45), Downing, Yakubu (Southgate 81).

Subs Not Used: Jones, Taylor.

Booked: McMahon, Hasselbaink.

Goals: Yakubu 52, 77.

Att: 19,877

Ref: P Dowd (Staffordshire).